Generally, a tire air pressure monitoring system receives radio wave sent by a tire air pressure sending unit, which detects a tire air pressure and sends tire air pressure information by radio. The tire air pressure monitoring system acquires the tire air pressure information from the received radio wave.
Referring FIG. 13, the tire air pressure monitoring system is used for a vehicle having a tractor head 101 and a trailer 102 which are connected with each other. In this case, the trailer 102 is connected with a rear portion of the tractor head 101 via a connection portion 111. The tire air pressure sending units 123 and 124 are respectively mounted in wheels 121 and 122 which are arranged at a rear portion of the trailer 102.
Trailer-side receiving units 125 and 126 are mounted at the trailer 102 to receive the radio signal containing the tire air pressure information, which is sent by the tire air pressure sending units 123 and 124. The received signal is outputted to a control unit 113 via wire harnesses 127 and 112 which are connected with each other at the connection portion 111. Based on the tire air pressure information in the received signal, the control unit 113 performs processes such as an indication of the tire air pressure information for a passenger in the vehicle, a storage of the tire air pressure information, a blowout alarm when the tire air pressure violently decreases, and the like.
Thus, in the case of the vehicle having the tractor head and the trailer which are connected with each other, the trailer-side receiving unit 125, 126 receives the radio signal from the tire air pressure sending unit 123, 124. Moreover, the received signal is outputted to the control unit 113 of the side of the tractor head 101 via the wire harnesses 127 and 112.
However, according to the above-described tire air pressure monitoring system, the receiving units 125 and 126 are to be mounted at the trailer 102 of the vehicle.
Moreover, the trailer 102 which is to be connected with the tractor head 101 is generally various. That is, the one tractor head 101 may be selectively connected with the diverse trailers 102, which are usually manufactured by suppliers different from that of the tractor head 101. In this case, it is necessary to accord a specification of an interface of the wire harness 127 of the trailer 102 with that of the wire harness 112 of the tractor head 101, between the different suppliers. Therefore, the construction of the trailer 102 for the tire air pressure monitoring system becomes complex.